Hydrogen is an important resource in the refining of crude oils and other hydrocarbon fractions. Refinery processes, such as hydrotreatment, hydrocracking, and catalytic dewaxing, can be dependent on the availability of hydrogen at a sufficiently high pressure as well as a sufficiently high purity.
Unfortunately, refineries tend to be net consumers of hydrogen. While processes such as reforming can result in generation of additional hydrogen, a typical refinery has greater demand for hydrogen than is available from processes in the refinery that generate hydrogen. External sources of hydrogen can be brought in to a refinery to make up the shortfall. However, such external hydrogen represents an additional (and potentially substantial) refinery cost, so any savings in the amount of external hydrogen consumed is beneficial.
One potential way to reduce the amount of external hydrogen needed can be to improve the use and recovery of hydrogen within a refinery. Refinery processes are typically performed using an excess of hydrogen, so that some hydrogen remains as an effluent or other product that exits a reactor. However, this hydrogen will typically have a higher level of impurities. Purifying and/or pressurizing this recycled hydrogen for use in the refinery can result in significant costs.
U.S. Pat. No. 7,632,476 describes a method for recovering carbon dioxide from a synthesis gas stream. Synthesis gas can be formed in a synthesis gas reactor, such as a steam reformer. A water gas shift reaction can be used to increase the amount of hydrogen in the synthesis gas. CO2 can be adsorbed from the output gas from the water gas shift reactor using an adsorbent system, such as an amine adsorbent system. After CO2 removal, hydrogen can be extracted from the output gas using a pressure swing adsorption system. Optionally, only a portion of the output from the water gas shift reaction can be diverted to the CO2 adsorbent system.
U.S. Patent Application Publication No. 2009/0117024 describes a process for hydrogen production with co-production and capture of carbon dioxide. A hydrocarbon reforming process can be used to generate a reformed gas stream. The hydrogen in a reformed gas stream can be removed first, such as by using a pressure swing adsorption unit. Carbon dioxide can then be separated from the hydrogen-depleted stream from the pressure swing adsorption unit.
U.S. Patent Application Publication No. 2010/0037521 describes another process for hydrogen and carbon dioxide production. A modified hydrocarbon reforming process is described that can increase the relative amount of CO2 in a high pressure syngas product relative to a lower pressure flue gas generated by the reforming process. The high pressure syngas product can then be sequentially passed through a CO2 recovery unit and a pressure swing adsorption unit for hydrogen recovery.
U.S. Patent Application Publication No. 2011/0011128 describes another process for hydrogen and carbon dioxide production. A hydrocarbon reforming process can be used to generate a stream containing hydrogen. The output from reforming can optionally be exposed to steam and a water shift catalyst to increase the hydrogen and carbon dioxide content of the stream. Hydrogen can then be separated from the stream using a pressure swing adsorption process. The system for the pressure swing adsorber can include multiple beds, with a conduit between beds. The multiple beds can optionally include different types of adsorbent material. For example, one bed can favor adsorption of carbon dioxide while a second bed can favor adsorption of methane. During the purge portion of the cycle of the pressure swing adsorber, the purge streams from the multiple beds can be separated, such as by withdrawing one of the purge streams via the conduit between the beds. The purge stream from the bed with greater methane adsorption can then be recycled as an input for the hydrocarbon reforming.